Large vertical reciprocating plunger pumps, such as the pump illustrated in FIG. 1 of U.S. Pat. No. 4,486,005 to Yaindl, normally have an upper pump section and a lower power section. The upper pump section includes a plunger connected to an upper crosshead, which is driven by side rods connected to a main crosshead in the power section. The power section of the pump includes a crankshaft mounted in a frame. One or more main crossheads are connected to the crankshaft by a corresponding number of connecting rods. The main crossheads are disposed between cradles in the frame which guide and confine the crossheads to linear reciprocating motion as the crankshaft is rotated about its drive axis.
The power section of conventional reciprocating plunger pumps is contained within and supported by a large box-like frame having side and end walls that carry both the primary vertical loads and the secondary lateral loads generated by the pump. The main crossheads are guided by cradles located on both side walls of the frame. The cradles on one side of the frame form an integral part of the frame side wall. These cradles, which are not removable from the frame, carry the secondary lateral loads generated by the pump. For maintenance purposes, the opposite side wall of the frame comprises a removable cradle panel. However, the removable cradle panel cannot bear the secondary lateral loads of the pump. Thus, the conventional reciprocating plunger pump can be operated only with the crankshaft rotating in one direction, i.e. toward the load-bearing cradle.
In addition to the unidirectional operating constraint of prior pumps, the conventional reciprocating plunger pump has other undesirable characteristics. For example, uniform casting of the large box-like frame is difficult because of the "closed" nature of the casting mold structure required. In addition, the overall length of a frame having integral cradles is necessarily greater than actually required. This is because the center-to-center distance of the integral cradles is dictated by manufacturing constraints such as boring tool swing clearances. This in turn requires a longer crankshaft with greater than desired distances between the main bearings, causing unwanted stress and wear to the power section components. Furthermore, because only the cradle panel on one side of the frame is removable, inspection and maintenance of the wear components of the power section are very difficult and time consuming.
Thus, it can be seen that there exists a need for an improved power section for large reciprocating plunger pumps, especially pumps having a multiplicity of plungers and main crossheads. In particular, a need exists for a large reciprocating pump frame which can be cast easily and accurately, which provides for individually removable crosshead guide cradles for ease of maintenance, and which allows the power crankshaft to be driven in either direction about its drive axis.